Iron and steel desulphurization



March 1, 1938. HEUER 2,110,066

IRON AND STEEL DESULPHURIZATION Filed May 9, 1935 5 Sheets-Sheet 2 \4 PQ N \1 n I x a 7 g Q "Q .L. Y 3

3g & 1 Lil Q/ 0 I k x g g I g hem! Jmzdfifkmflw March 1, 1938. R. P.HEUER IRON AND STEEL DESULPHURIZATION 5 Sheets-Sheet 3 Filed May 9, 1935March 1, 1938. HEUER 2,110,066

IRON AND STEEL DESULPHURIZATION V Filed May 9, 1955 5 Sheets-Sheet 5$4.46 (mzmum suLPuuR) sLAG (HIGH .suLPuuR) oxlnlzms SULPHUR l or MOLTENsLAe S LPHUR DIOXIDE .sLAG (LOW SULPHUR) sue (msmum summon) 5LA6 (MEDIUMSULPHUR) aLAs (man Summon) I REDUO ING T0 POWDER mom I ROASTING (uemumME LTING AND REACTION sue (LOW sumnuR) j (LADLH mom SLAG (MEDIUMSULPHUR) I nvsumu Z 6 IRON .sLAs (MEDIUM sumnun) IGH sumo 596 (menSULPHUR) CARBON NR MATTE-FORMING Mew.

Low m SULPHUR "i MIL-n OXIDATION l mow MATTE RJRMING METAL (mzmum man In5ULPHUR suLmuR) I srnoue oxmAnoN a owsu P $44 (I. L HUR) CARBON LADLE;mun LAs (manwm suLPnun) 4|.owsu|.mu|? I M r Ww: WMMM Patented Mar. 1,1938 I 2,110,066

UNITED STATES PATENT OFFICE IRON AND STEEL DESULPHURIZATION RussellPearce Heuer, Bryn Mawr, Pa. Application May 9, 1935, Serial No. 20,555

36 Claims. (01. 75-55) The invention relates to the manufacture ofcontent and therefore limited in its ability to pig iron and theproduction of steel, and partake up sulphur from the pig iron, and,after ticularly to the desulphurization of pig iron. removal of thefirst slag, treating the pig iron A purpose of the invention is to lowerthe cost with one or more further slags of lower sulphur of pig ironproduction in the coke blast furnace content and correspondingly greaterability to 5 by operating the blast furnace at lower temperaremovesulphur. In this way, pig iron containture and/or with less basic slag,thus obtaining ing substantially more than 0.10% of sulphur, pig ironabnormally high in sulphur compared say 0.3% of sulphur or more, canhave its sulto present practice and substantially higher in phur contentreduced to less than 0.05% sulphur sulphur than that ultimately desired,and to treat (that is, to less than half) by treatment for an 10 themolten pig iron external to the blast furnace hour or more with slagswhich aggregate less hearth with a basic slag which is free-flowing than8%, for example, only about 5%, of the below 1400" C. to remove sulphurwhile positively weight of the pig iron. maintaining a strong reducingcondition in the A further purpose is to desulphurize molten slag. Thepig iron thus produced may be used pigiron with a slag capable ofabsorbing sulphur 15 in the form of cast iron, or used as a rawrmateupto-a percentage in the slag at least one hunrial, for example, formaking steel. dred times the percentage present in the desul- A furtherpurpose is to desulphurize molten phurized pig iron, to separate theslag from the pig iron in the presence of an excess of carbon,desulphurizing vessel and from the molten pig preferably as a carbonlining, by a reducing slag iron and to revivify the slag while it is outof 2 while excluding oxidizing gases. contact with the molten pig ironto permit the A further purpose is to desulphurize pig iron reuse of theslag for desulphurizing more iron. objectionably high in sulphur,obtained by eco- The preferable slag for this purpose consists nomicaloperation of the coke blast furnace, by mainly of lime and fluorspar.

treating the pig iron in molten condition with a A further purpose is todesulphurize molten pig 25 basic desulphurizing slag freely flowing at1200 iron in a stepwise manner by initially treating it C., anddesirably containing more than of with a first slag relatively high insulphur which oxides of the R10 type, where R. is a metal of the H hasbeen used to desulphurize a previous charge alkaline earth or alkaligroup, preferably calof pig iron and not since revivified and by subse-30 cium but permissibly strontium, barium, sodium, quently treating itwith a second slag which is 30 etc., and :r is the numeral 2 or 1depending upon relatively low in sulphur, revivifying each slag thevalence of the metal B. when its sulphur content becomes high enough Afurther purpose is to agitate pig iron during to prevent efficientdesulphurization. In nonnal desulphurizing treatment with a basic slagunder operation, the first slag after use is immediately reducingconditions and with the exclusion of revivified and the second slagafter use is pre- 35 oxidizing substances. served for treatment of thenext pig iron charge A further purpose is to desulphurize molten pigbefore revivification. iron excessively high in sulphur by treating itin A further purpose is to revivify a pig iron dea closed vessel with abasic desulphurizing slag sulphurizing slag by separating the slag fromthe in the presence of an excess of a noncontamidesulphurizing vesseland from the molten pig 4o nating reducing gas such as carbon monoxide,iron and thereafter driving oil? sulphur from the which serves toexclude oxidizing gases such as slag as a, volatile sulphur component.air and to maintain the reducing conditions A further purpose is torevivify pig iron derequisite to desulphurization. Thenoncontamisulphurizing slag and to recover elemental sulnating reducingas such as carbon monoxide is phur or a sulphur compound from therevivified 45 desirably under sufficient pressure to prevent inslag,thus permitting reuse of the slag for further filtration of air, and itmay be mixed with nitrodesulphurizingand crediting of the value of thegen and/0rnon oxidizing quantities of carbon recovered sulphur orsulphur compound against dioxide. the cost of the process.

A further purpose is to economize upon the A further purpose is todesulphurize molten 50 use of desulphurizing slag in any of theprocesses pig iron by a slag in such manner as to protect disclosedherein by efiecting the desulphurizing the slag from the influence offree oxygen, pretreatments in stepwise manner, preferably inidominantlyoxidizing oxides of carbon and water tially subjecting the pig iron to afirst desulphurduring the desulphurizing step, to subsequently izingslag which is relatively high in sulphur treat the sulphur-bearing slagin the presence of 55 carbon dioxide and water to remove its sulphurcontent and to use the treated slag to desulphurize additional pig iron.

A further purpose is to reduce pig iron desulphurizing slag containingan alkaline earth sulphide such as calcium sulphide to a powder, to makeit up into a slurry with water andto subject the mixture of water andpowdered slag to the action of carbon dioxide gas to revivifythe slag.The carbon dioxide gas may preferably be obtained from the products ofcombustion of blast furnace gas.

A further purpose is to drive off sulphur from a pig iron desulphurizingslag containing an alkaline earth sulphide by treating the slag withcarbon dioxide and water to generate hydrogen sulphide, and to burn thehydrogen sulphide either with sufficient oxygen to produce sulphurdioxide, or with the required amount of oxygen to obtain elementalsulphur.

A further purpose is to produce a' pig iron desulphurizing slag which isfluid at 1200 C. and which has the property of self-disintegration whenit solidifies and cools, to facilitate revivification of the slag andavoid the necessity of pulverizing the slag.

A further purpose is to desulphurize pig iron by a free-flowing basicslag, to separate the slag from the desulphurizing vessel and torevivify the slag by blowing a gas containing free oxygen through theslag in molten condition to oxidize the sulphur.

A further purpose is to revivify pig iron desulphurizing slag containingcalcium sulphide or the like by reducing the slag to a powder, roastingthe slag to produce calcium sulphate, mixing the roasted slag with theproper amount of slag containing calcium sulphide and calcining themixture at a sufliciently high temperature to drive off sulphur dioxide.

A further purpose is to revivify pig iron desulphurizing slag bybringing the slag into contact with a molten matte-forming metal, suchas copper, under mildly oxidizing conditions, and, after thematte-forming metal is separated from the slag, vigorously oxidizing thematte-forming metal to remove the sulphur.

A further purpose is to make up a pig iron desulphurizing slagcontaining from 30% to 55% of lime,'from 20% to 50% of fluorspar andfrom 5% to of silica, and preferably containing about 45% of lime, about40% of fluorspar and about 15% of silica, the slag being freelyflowingat- 1200 C.

A further purpose is to pour pig iron into :a desulphurizing vesselthrough a pouring head which excludes the air, and which preferably hasan ofi-center inlet into a circular pouring opening.

A further purpose is to desulphurize pig iron in a ladle car having acarbon lining, and desirably provided with means for agitatingthe moltencontents of the ladle car.

A further purpose is to use the pig iron desulphurized in the novelmanner disclosed herein I for the manufacture of steel, preferably as acontinuous process in which the iron remains molten-from the time itleaves the blast furnace until the time that it leaves the steel-makingfurnace.

Further purposes appear in the specification and in the claims.

The invention relates not only to the process involved, but also to theslag employed and to the apparatus used.

2%, with varying contents of metalloids.

The apparatus is claimed in my application Ser. No. 171,800, filed Oct.29, 1937.

The drawings are largely diagrammatic illustrations preliminarilyintended to aid in understanding the invention, or to disclose apparatuswhich may be employed in performing the process. All apparatus shown isstrictly schematic, and no effort has been made to complicate thedisclosure by the illustration of detail within the routine skill ofthose in the art.

Figure 1 is a diagram whose ordinates are the square roots of activitiesof sulphur from dissociation of iron sulphide. The absclssae areabsolute temperatures.

Figure 2 is a diagrammatic side elevation of a desulphurizing vesselwhich may be used in practicing the invention.

Figure 3 is a left end elevation of the structure of Figure 2. 4 v

Figure 4 is a transverse section of Figure 2 upon the line 4-4 thereof.c

Figure 4a is a fragmentary view corresponding to a portion of Figure 4,with a door substituted for the pouring head.

Figure 5 isa horizontal section of Figure 4 on the line 5-5 thereof.

Figure 6 is a chart of a desirable process of desulphurizing pig ironand revivifying the slag in accordance with the invention.

Figures 6a, 6b, and 6c are charts of various processes of revivifyingthe slag in accordance with the invention.

Figure '7 is a. diagrammatic view of apparatus which, may be used forrevivifying the slag. Y

In the drawings like numerals refer to like parts, and in thespecification'like symbols refer to like subject matter.

Throughout the specification, wherever reference is made to pig iron, itis intended to designate the product of the blast furnace whichcharacteri'stically has a high carbon content, usually of 3% to 4%, ormore, and always in excess of The product of the blast furnace isreferred to as pig iron whether it is intended to be used in the form ofcast iron or whether it is to be used in making steel.

In the production of pig iron from low-sulphur burdens (such as woodcharcoal and low sulphur ores) it is unnecessary to operate the blastfurnace in such a manner as to obtain strong desulphurizing conditionsin the hearth and bosh of the blast furnace. As a result the operationof the charcoal blast furnace is quite economical except for theexcessive costs of charcoal and of low sulphur ores. In most instances,however, because of the high cost of wood charcoal, it is necessary tosubstitute coke for wood charcoal as a blast furnace fuel. When this isdone, a strong desulphurizing action must be obtained in the hearth andbosh of the blast furnace in order to obtain a product having low enoughsulphur to be commercially usable. For a strong desulphurizing action,it is necessary to have a higher temperature and a slag containing morelime. More fuel must be used in order to provide the higher temperature.

A typical slag from a charcoal blast furnace approximates where In theabove slag the silica exceeds the lime plus magnesia. The sulphur in thepigiron approximates 0.02%.

A typical slag from a coke blast furnace has the following approximatecomposition Per cent SiOz 34.0 A1203 12.0

CaO 40.0

MgO 10.0

In the above slag the silica is less than the lime plus magnesia. Thesulphur in the pig iron ap-- proximates 0.03%

The temperatures of the slag and pig iron tapped from a charcoal blastfurnace are about 1450 C. and 1410 C. respectively. In the coke blastfurnace, the respective temperatures of the slag and pig iron as tappedare approximately 1525 C. and 1475 C. Thus it is unnecessary for thecharcoal blast furnace to expend as much heat to produce slag and pigiron as does the coke blast furnace.

From the above data it will be obvious that the cost of removing sulphurfrom the pig iron simultaneously with smelting of the ore in a blastfurnace is considerable. It is one purpose of the present invention tocheapen the cost of manufacturing pig iron, whether for use as cast ironor for making steel, by omitting the strong desulphurizing action nowconsidered necessary in the coke blast furnace because of thesulphurbearing burdens. The iron is very desirably smelted in the cokeblast furnace under conditions similar to those prevailing in charcoalblast furnaces, using a blast furnace slag in which the silica exceedsthe lime plus magnesia. The smelting is conducted in the coke blastfurnace under conditions of temperature and basicity of slag suitable toproduce pig iron at lower cost but with a higher sulphur content in theiron than that ultimately desired. The sulphur content in the ironproduced may be for example 0.25% sulphur. After production of this highsulphur pig iron, it is treated in novel manner as a wholly independentoperation to remove the excess of sulphur. The cost of thedesulphurization is small and it is possible to produce pig iron ofdesirable quality at a considerable saving.

The pig iron, containing a higher sulphur content than that ultimatelydesired, is transferred from the coke blast furnace to a suitabledesulphurizing vessel as described later. The pig iron is theresubjected to a strongly basic slag under reducing conditions. It isgenerally considered that the sulphur in pig iron is present as FeS.This iron sulphide will dissociate thus:

Due to this dissociation, there is a certain activity of sulphur in themolten pig iron which is measured at constant temperature by theequilibrium constant for equation (1), thus Fe)( S3) AF.S 1 2)(AFe)=aCt1 Vity of iron (A3 =activity of sulphur (Ares) =activity ofiron sulphide v K1=equilibrium constant The iron sulphide is consideredto be present in solution in the molten pig iron and its activity variesas the concentration. The relation of sulphur activity and sulphurconcentration is expressed in Figure 1, taken from H. Schenck,Physikalische Chemie der Eisenhiittenprozesse (Verlag von JuliusSpringer, Berlin, 1932) volume 1, page 263. In this figure, theordinates are square roots of the activities of sulphur fromdissociation of iron sulphide and the abscissae are temperature indegrees absolute (K.). The curves are plotted for an iron-sulphur systemfree from carbon.

Within the area D C E F G H I, iron sulphide and iron occur as liquidsolutions. In these solutions the sulphur activity is a function of thesulphur concentration. In Figure 1, diagonal dotted lines are showncorresponding to the sulphur percentages indicated by the numerals tothe right of the dotted lines. The sulphur activity resulting from agiven sulphur percentage in the melt and a given temperature is shown bythese dotted lines. It would require a third dimension to show therelation of sulphur activity, sulphur concentration and temperature forliquids containing iron, iron sulphide and carbon. As an approximationfor example to conditions prevailing in molten pig iron of 0.02% sulphurcontent at 1400" C. (1673 K.) we may extend the line for 0.02% sulphuroutside the area D C E F G H I and into the area B C E F G until thetemperature 1673" K. is reached and learn that at J the equalsapproximately 10 for 0.02% sulphur at 1400 C.

From Figure 1 it will be seen that, as the pig iron is subjected toconditions which lower the sulphur activity, the sulphur content willfall.

-The desulphurizing slag contains basic oxides of the alkaline earth oralkali metals such as calcium oxide, barium oxide, strontium oxide,sodium oxide, etc. These are referred to generally as R10 oxides, whereR is an alkaline earth or alkali metal and :c is the numeral 2 or 1,depending upon the valence of the metal. The oxides of the slag tend toreact with sulphur of the pig iron thus:

For this reaction the equilibrium at constant temperature is expressedthus:

( R,s2- o From reaction (3) it will be evident that there will be a lowactivity of sulphur and sulphur can be removed from the pig iron toenter the slag most efliciently if there is a low oxygen activity.

- In other words, the sulphur activity may be lowered directly bylowering the oxygen activity. The desulphurizing slag is thereforecaused to act upon the pig iron in the presence of a reducing agent,preferably an excess of carbon. The carbon produces a low oxygenactivity according to the reaction:

The equilibrium expression for this reaction is has been found to bevery satisfactory. Such a (AC0) slag can be readily synthesized bymixing lime m=i 3 (6) and fiuorspar of commercial grade, adjusting the csilica to the desired percentage by the addition of where silica sand,after allowing for the silica present (A0) =activity of carbon asimpurity in the lime and fiuorspar. Magnesia (A00) =activity of carbonmonoxide present as a normal impurity in a good grade of Ka=equilibriumconstant a lime is not objectionable. Alumina present as a Theequilibrium constant K: may be calculated small amount of impurity isalso not objectionfrom the Gibbs free energy of reaction (5) by able.Indeed the addition of approximately 5% the equation: of alumina seemsto be advantageous as itre- 1n K3 (.7). duces somewhat the melting pointof the desulphurizing slag. The above slag flows freely at Where 7 1200C. and this property is very desirable for et- AF free energy changeflclentdeslllphulizatlon.

R=gas constant Molten pig iron high in sulphur (0.25% S) has T=absemtetemperature been subjected to the action of the lime-fiuorsparsilicaslag above referred to at 1400" C. for one The r energy change-at giYentemperature hour in a refractory container composed of caris expressedthe following equation taken -bon in the form of graphite. The slag andmolten from International Critical Tables, volume VII, pig mm were underStrong reducing conditions Page 243: and the desulphurizing-vessel wasarranged so as APO: 2 00 2 15 T m to prevent direct contact with theatmosphere or 0.00215 2 0 0000002 a g,20 (8) with combustion gases highin oxygen, .carbon dioxide or water. Under these conditions the slag At1673" K. (1400 C.) the free energy change picked up as much as 79sulphur and t 1,93 pig iron had its sulphur content reduced to 0.03%sulphur, so that there was more than one hundredsubstltutmg this Valuein Equations (7) and (6) (in fact more than two hundred) times as high aand assuming that the activities of carbon and sulphur percentage inslag as m the pig iron carbon monoxide in Equation (6) are unity sinceafter desulphurization. In other cases in which the carbon is present inexcess and is available the pig iron initiauycontamed only about 093%tofiupply an excess of carbon monoxide it 15 sulphur, the sulphurcontent of the pig iron was evident that the oxygen activity of the slagin reduced to 0 o02 sulphur and the slag picked up the presence ofexcess carbon can be reduced at sulphun These results indicate that avery equilibrium to v strong desulphurizing action is obtained in the (A)}=8 2 100 above manner, and that the sulphur content of .the iron maybe reduced to less than one-half, or If, for the purpose ofillustration, it be asless than one-quarter, or even less than one-tenthsumed that it is desired to desulphurize pig iron of that in the ironbefore treatment by my invenuntil the sulphur activity reaches a pointat tion. which Slags higher in lime than 45% may be used; for

(A 914: 10- example, a slag containing Per cent Equation (4) may besolved using this value of Cao 55 (A CaF- 33 l S102 12 and thepreviously determined value of A K is a. very eflicient desulphurizer.It will be noted that this slag contains more than twice as much thusalkaline earth oxides as silica.

( n,s)-( X10') With rising lime content the viscosity of the W 2 (9)slag increases and therefore excessive lime content is to be avoided.Where a lime fiuorspar a s) slag is to be employed, the lime contentshould (10) be from 30% to 55%, the fiuorsparcontent from 20% to 50% andthe silica content from 5% to (A )=(I.2XIO )(A O)K2 (11) 25%. Adesirable slag may contain lime in excess of 130%, fiuorspar in excessof 20%, silica in fig of (Ams) isa'mea'sure of the q f excess of 5% andalumina from 1% to 5%, the

or percentage of B13 in the desulphurizing composition being ad usted tomake the slag slag. For most economical desulphurization it is f eel flwi at C or at least free flowm desirable to have a high ratio of sulphurin the a C g slag tqsulphur m the mg iron that n A study has been madeof the use of soda slags percentage of Rats in the slag whendesulphrizaa mm is finished This is accomplished by keep as a substitutefor lime slags. The desulphurizing the product (AR )K hi h thr ingaction of soda, for example sodium carbon- :0 2 g ough choice of t i i nk d mi 8 b aslag of proper chemical composition. 2 on pg "9 s we nown ans u stitution can be made. It is found, however, that slags pure soda isreadily attacked by carbon at temperatures of 1400 C. or even below,producing A desulphunzmg slag having the composition sodium vapor whichis very effective in convert- Per cent ing FeS into NazS and thusdesulphurizing the CaO 45 pig iron. The sodium vapor causes diflicultyin CaFz- 40 the handling of soda slags, and the reaction must SiOz 15 bemanaged in such a way as to limit the formathe case of lime slags.

Detailed reference to the steps necessary when soda slags are used istherefore omitted, and the further discussion is generally confined toslags containing alkaline earth oxides as the preponderant activeconstituent. However, the use of slags containing soda or other alkalimetal oxides as active desulphurizing ingredients, when used assubstitutes for slags containing alkaline earth oxides such as lime asactive ingredients, is claimed herein.

The quantity of oxides of the type R10 in the slag should exceed 30% forbest results.

Due to the cheapness and freedom from volatilization, it is preferableto use a. lime slag, although such preference is subject to change undervarying economic and metallurgical conditions.

In choosing the slag, it is desirable to have one which will be of lowviscosity and workable at temperatures of 1400 C., and, for thispurpose, the slag should preferably be freely fluid as low as 1200 C.

It is very advantageous to use a slag which shows a high ratio ofsulphur concentration in the slag after use to sulphur concentration inthe desulphurized or partially desulphurized pig iron. If, for example,0.25% sulphur must be removed from the pig iron and if the slag willtake up as much as 12.5% sulphur, then one ton of slag will desulphurize50 tons of pig iron.

As noted in detail below, it is quite important to employ a slag whichcan be revivified or treated to remove its sulphur so that it can beused over and over again. The lime slags re-' ferred to above fulfillthis requirement.

The desulphurizing slag, after it has picked up, for example, 12%sulphur, is revivified by removing the sulphur, until, for example, lessthan 1% sulphur remains. This revivified slag is then used repeatedly todesulphurize further quantities of molten pig iron. The revivificationof the slag may be accomplished in one of several ways discussed below.

Desulphurz'zation The pig iron used in the process will in most cases bepig iron produced in the coke blast furnace when operated underconditions of moderate temperature and moderate basicity of the slagsuitable to produce pig iron at lower cost but with a higher sulphurcontent than that ultimately desired. The sulphur content of the pigiron produced in the coke blast furnace under such economical conditionsmay be 0.25%, 0.3% or even higher. Of course the invention may also beapplied to pig iron of normal sulphur content, containing say 0.04% S.The pig iron is tapped from the coke blast furnace, and, of course,separated from the blast furnace slag at the time of tapping. The pigiron is then preferably brought at once into contact with thedesulphurizing slag, while the pig iron is still molten from the blastfurnace.

The actual desulphurization may, for example, be carried out in a vesselsuch as that shown in Figures 2 to 5, inclusive, whichillustrate a ladlecar of the general type disclosed in Pugh U. S.

Patent No. 1,534,187, granted April 21, 1925. The ladle car comprises aladle body 20, covered with a metallic casing 2| having a cylindricalcentral portion 22 and conical end portions 23 and 24 which terminate inheaders 25 and 26. The headers support trunnions 21, 21, 21 and 21 whichengage bearings 28, 28', 28 and 28 The bearings 28, 28', 28 and 28 aresupported from a main frame 29, which in turn rests upon any suitablerailway trucks 30 and 3|, operating upon a track 32.

To permit tilting or rocking of the ladle car, the main frame 29 isbowed at 33. The hook of a crane may be engaged with the main frame, asat 34, to lift one side of the main frame, causing trunnions 21' toleave bearings 28' and eventually causing trunnions 2'! to engagebearings 28 The lifting and lowering of one side of the main frame maybe used to agitate the liquid contents of the ladle car, and may also beused in tapping the ladle car.

The means of rockingand tilting the ladle car need not be-that shown, asany other suitable means may be employed. For example, the reactionvessel of the ladle car may be rotated by a conventional driving bandand motor as shown, for example, in Hart U. S. Patent No. 1,916,170,granted June 27, 1933.

Inside the casing 2| is a lining 35 of suitable refractory material. Itis contemplated that this will normally be a carbon refractory such asgraphite, although any other suitable lining material, such asmagnesite, for example, might be used. If carbon be used as a lining, itmay be rammed in place with a tar binder or built into the desired formfrom blocks which have previously been fired.

Inlet to the ladle car is provided through a charging opening 36 whichis engaged by a pouring head 31 detachably secured at 38 to the easing2| and making a seal at 39 about the charging opening. The pouring head31 desirably has a conical interior as shown in Figure 4. A runner orlaunder 40 suitably detachably connected to a coke blast furnace 4|enters the pouring head 31 at one side thereof as indicated at 42 sothat pig iron flowing along the runner 40 enters the pouring head at 42and receives a circular motion before entering the ladle car.

The discharge of slag from the ladle car is facilitated by a pouringspout 43 below the charging inlet. When the pouring spout is used, theladle car will be tilted, and the pouring spout will normally be closedwhen not in use by a plug 44. The ladle car is provided with an inletconnection 45 for noncontaminating reducing gas as later described. Asimilar inlet opening 46 is desirably provided in the top of the pouringhead so that a constant small escape of noncontaminating reducing gastakes place at the point 42 where the blast furnace runner enters thepouring head. The pouring head is equipped with lifting rings 41 tofacilitate removal from the ladle car. When the pouring head is removedadoor 48 is substituted to close the charging opening as shown in Figure4a, and to prevent the introduction of air and gases of combustion highin oxygen, carbon dioxide or water vapor which would be oxidizing.Access to the interior of the ladle car for inspection purposes isprovided through doors 2|.

Though not'normally needed, the ladle car is equipped with suitable setsof electrodes 49 and 49' which may be connected to a suitable source ofelectrical energy to supply are heating of the is charged in solid form.

ladle car. The electrodes are detachably connected to the ladle car, asat 50, and they may be removed and a door substituted to close theopening. In most cases no heating is necessary or desired, as the moltenpig iron when charged into the ladle car has sufllcient superheat tomaintain itself freely molten during the desulphurization and to meltthe slag where the slag Any other form of heating which isnoncontaminating may be used instead of electric arc heating, if heatingbe desired.

It will of course be understood that, where an arc is not used, calciumcarbide will not be formed in the slag.

An illustrative cycle of operations is indicated in Figured. Thespecific values given on this figure vary somewhat from those mentionedin other examples, and are given as a particular instance of theprocess, without intention to limit the disclosure.

The ladle car containing about 2.5 tons of molten slag, preferably slagwhich has previously been used to desulphurize a previous charge ofmolten pig iron, is filled with about 100 tons of molten pig iron fromthe coke blast furnace flowing through the blast furnace runner 40, andcontaining as much as 0.3% sulphur or more (say 0.26% sulphur). Themolten slag is held in contact with the molten iron for as much as onehour or more until the sulphur content of the molten pig iron has fallento about 0.03% sulphur to 0.10% sulphur (say 0.05% sulphur) and thesulphur in the slag has increased to perhaps sulphur or a much higherfigure (say 10.8% sulphur). With good operating con-' ditions andefficient slags,-as much as 12% sulphur can be built up in the slag withonly 0.04% or 0.05% sulphur in the pig iron. It is desirable 'to have ahigh concentration of sulphur in the tion of the moltenpig iron isaccomplished. The

pig iron and slag are maintained in contact with one another preferablyfor .an additional hour or more, and the sulphur content of the metalmay thereby be reduced to 0.015% sulphur, 0.01% sulphur or even less ifdesired. The.

sulphur content of the second slag may increase from a negligiblequantity at the time it is charged to 1% sulphur or 2% sulphur or more.

The molten iron is then separated fromthe second slag, as by tapping thesecond slag, then removing the molten iron, and then pouring back thesecond slag into the ladle car, or by retaining the molten slag in theladle car during tapping of the iron, for example by submerging thepouring opening below the slag level before removing the plug from thepouring opening and then retaining the slag level above the pouringopening during pouring from the ladle car.

The ladle car is then returned to a source of high sulphur pig iron toreceive a further charge of say 100 tons, and the further charge isdesulphurized by a first treatment with the slag which was used as the'second slag on the previous charge, removal of the high sulphur slagproduced thereby, addition of fresh slag and so on. v

It will of course be understood that a stationary ladle, mixer or.furnace can be employed, if it is suitably equipped to maintainsufilciently reducing conditions and, in the preferred process, excludeoxidizing gases such.as free oxygen, predominantly oxidizing oxides'ofcarbon and water vapor in high concentration.

The amount of slag required per ton of pig iron desulphurized willdepend on the amount of sulphur to be removed from the pig iron and theamount 'of sulphur picked up by the slag. If, for example, a highsulphur pig iron containing 0.26% sulphur is desulphurized to 0.015%sulphur, then, for every 100 tons of pig iron, 0.245 ton of sulphur mustbe taken up by the slag. If the slag picks up 9.8% sulphur, 2.5 tons ofslag will be necessary to treat 100 tons of pig iron.

In desulphurizing high sulphur pig iron, a stepwise process as describedabove is quite efflcient since it removes the sulphur with a small- .eramount of slag, and necessitates regeneration of a smaller amount ofslag for further desulphurization. For efiicient desulphurization theratio of the percentage of sulphur in the slag to the percentage ofsulphur in the pig iron after desulpherization may be as much as'250 to1 or even a higher ratio. slag incontact with-molten pig iron having0.015% sulphur might have picked up 2.5% sulphur from the pig iron(corresponding to about 6% calcium sulphide). If 100 tons of iron werebeing treated'to remove 0.25 ton of sulphur, 10 tons of slag might beneeded if the desulphurization were done in a single step.

If the pig iron were desulphurized in a stepwise process as shown inFigure 6, reducing the sulphur first to about 0.05% sulphur andseparating a sulphur-rich slag containing 10.8% sulphur, then adding asecond and fresh slag to remove the balance of the sulphur in the irondown to 0.015% sulphur, then separating the iron from the second slagcontaining about 2.4% sulphur (corresponding to about 6% calciumsulphide) for use in the preliminary treatment of the next charge ofsulphur-rich pig iron as above described. the removal of 0.245 ton ofsulphur from 100 tons of iron can be accomplished with only 2.5 tons ofslag, although'3.5 tons of slag, or more, may be used.

By stepwise treatment it is possible to reduce Thus a desulphurizing thesulphur content of molten pig iron from a value in excess of 0.10%, say0.3%, to less than 0.01%, in one or two hours, by slags which aggregateless than 8% and generally not more than 5% of the weight of the pigiron.

For best results the slag used should be very liquid at the temperatureprevailing. It was found that 1400 C. was an economical and desirabletemperature, although higher or lower temperatures may be used. If theslag flows freely at 1200 C., it will of course bevery liquid at 1400 C.A very satisfactory slag may con-' tain CaO 45%, Cal: 40% and S10: 15%..In

order to lower the slag fusion point, a little alumina may be added, forexample using a composition of CaO 43%, CaFa 38%, SiOz 14% and A120: 5%.With a slag of the character of one of those just noted, it is possibleto absorb 10% or more of sulphur in the slag, and, under favorableconditions, to obtain a ratio of the percentage of sulphur in the slagto the percentage of sulphur in the iron at the end of desulphurizationexceeding 250 to 1.

In the case of a lime slag, sulphur is retained FeS- Fe+ 82 (1) Thesulphur reacts with the lime or other RO oxide of the slag thus To drivethe above reaction to the right and desulphurize the pig iron it isnecessary to keep the oxygen activity low by reducing agents. The highcarbon content of the pig iron itself has some reducing action, and itis decidedly preferable to desulphurize the iron while it still has itspig iron carbon content to aid in reduction than at a later stage whenits carbon content has been lowered, for example to that of steel.

It is preferable to employ a carbon lining in the ladle car, and thisserves to assist materially in maintaining reducing conditions. It isalso very desirable where a. carbon lining is used, and much moreimportant where a carbon lining is not used, to introduce coke orcharcoal into the slag, maintaining a substantial body of carbonfloating on the molten pig iron. In the slag 5| floating on the moltenpig iron 52 carbon is seen at 53.

The carbon lined ladle car is desirably so constructed as to positivelyexclude oxidizing gases, such as air, predominantly oxidizing mixturesof oxides of carbon, or water vapor, for example from products of fuelcombustion. Exclusion is accomplished not only by the closedconstruction of the ladle car, but also by the pouring head 31, and thedoor 48 when the pouring head is not in place.

As a further assurance against introduction of air, oxidizing mixturesof oxides of carbon or water vapor into the interior of the ladle car,and as a protection against burning of the carbon lining, it is possibleto introduce a noncontaminating reducing gas into the ladle car and alsointo the pouring head. The gas should suitably be maintained atsuperatmospheric pressure so that leakage through the inevitable cracksin the structure will be outward. The gas may suitably comprise carbonmonoxide or a. mixture of carbon monoxide, carbon dioxide and nitrogenwhich is preponderantly reducing due to the large proportion of carbonmonoxide compared to carbon dioxide. Such a reducing gas consisting of apreponderantly reducing content of carbon monoxide, a small quantityofcarbon dioxide whose oxidizing effect is more than overcome by thecarbon monoxide and a large inert content of nitrogen may be obtainedfrom the coke or charcoal gas producer. Where steel is to be made,hydrocarbon reducing gases may be used'without harm.

If other reducing agents than carbon be desired to remove oxygen inReaction (12) calcium carbide, ferro-silicon, orother reducingferro-alloys may be added to the slag. The lower the oxygen activity,the higher the possible ratio of sulphur in the slag to sulphur in thepig iron at the end of desulphurization, the more complete thedesulphurization and the more rapid the reaction.

To facilitate the desulphurization, agitation of the metal and slag maybe used. Such agitation may be produced by rocking or rotating the ladlecar, by raising and lowering one end of the ladle car asthough runningthe car over an uneven track, introducing wood poles or rabbles into theladle, blowing reducing gas such as carbon monoxide or hydrocarbons(where steel is to be made) through the molten mass, etc.

The presence of an excess of carbon monoxide at the point ofdesulphurization is of course assured by blowing a gascontaining carbonmonoxide upon or into the molten charge, although the same result isobtained by maintaining an excess of carbon in contact with the moltenpig iron and/or slag, or by maintaining carbon 'monoxide gas on thesurface of the molten charge.

The gas used either on the surface of the molten charge or to blowthrough it may be coke or charcoal producer gas which contains apredominantly reducing mixture of oxides of carbon plus nitrogen. v1

The desulphurized pig iron from the ladle car may be used in any form inwhich pig iron is suitably employed, as for example for gray iron ormalleablized castings, etc. It is contemplated, however, that a largepart of the desulphurized pig iron will be used in steel-making furnacesfor the production of steel in much the same manner that theconventional low sulphur product of the coke blast furnace is now used.

Where steel is made, the economy in production of the raw material willeffect an over-all economy in the steel process. A further importantadvantage in steel making is that it will in no case be necessary totake any precautions in steel making to eliminate sulphur, as issometimes necessary when the blast furnace pig iron runs excessivelyhigh in sulphur. This is of especial importance in the manufacture ofelectric steel, in which case sulphur elimination takes a substantialpart of the time and contributes to the cost. Nor will it be necessaryto reject certain ores or coke on account of the sulphur content whensmelting pig iron for steel-making purposes.

The detail of the refining of the pig iron to make steel is not part ofthis invention, and the desulphurized pig iron may be used in the acidor basic open hearth, the electric furnace, the Bessemer converter or inany other suitable manner to produce steel.

Revim'fication There are several ways of revivifying the desulphurizingslag of the invention to lower its sulphur content so that the slag maybe used again to desulphurize a further charge of pig iron, and so thatthe sulphur may be recovered. It is contemplated that the desulphurizingslag may be used repeatedly to treat further quantities of pig iron,with revivification when the sulphur content becomes so high thatfurther desulphurization is impeded, and with addition of fresh slagwhen the losses of slag necessitate augmenting the quantity. It will benoted that, in

accordance with the invention, the conditions are always reducing whenthe desulphurizing slag is in contact with the molten pig iron, thusminimizing the picking up of phosphorus, manganese, etc., by the slag.If the slag were in contact with the iron when oxidation was possible,pick-up of phosphorus, manganese, etc., by the slag would be excessive.Naturally, a substantial pick-up of phosphorus, for example, wouldrender the slag unusable even though it were revivified to lower itssulphur content, and therefore it is important to avoid having contactbetween the molten pig iron and the desulphurizing slag under unsuitableoxidizing conditions. i

The slag is revivified while it is out of contact with the molten pigiron, and preferably after separation from the desulphurizing vessel, asrevivification involves oxidizing reactions which would be harmful todesulphurization.

It is preferred to effect the revivification by the principlesunderlying the process of Claus and Chance as used for removing thesulphur from calcium sulphide present in tank wastes producedv in the LeBlane soda'process. See George Lunge, Sulphuric Acid and Alkali (D. VanNostrand 00., N. Y., 1909) volume 2, part 2, page 943 et seq. Thisrevivlfication process applies to slags containing any of the alkalineearth sulphides, but calcium sulphide, being the cheapest, is referredto below in the specific example. In accordance with this process thedesulphurizing slag containing perhaps 35% of calcium sulphide isreduced to a fine powder, preferably to a state of subdivision such thatit will pass through a 50 mesh per linear inch (387.5 mesh per squarecentimeter) screen. It is of course possible to reduce the slag to apowder by crushing and grinding and such a step is indicated on theprocess chart of Figure 6. It has been found, however, that it is agreat convenience and economy to use a slag which isself-disintegrating, due to the volume changes which the alkaline earthsilicates undergo when slowly cooled. The slag comprising Percent CaO'45 CaFz 40 $109 15 is self-disintegrating, as it breaks up into a finepowder when cooled slowly to room temperature. The following slag isalso self-disintegrating Percent CaO 55 Cal: 33

cas+nzo+cowcacog+ms V (13) Thehydrogen sulphide liberated maythen reactCaS+HzS Ca(SH) 2 (14) Further treatment with carbon dioxide causes thereaction Any suitable source of carbon dioxide may be employed. As asource of carbon dioxide which is very convenient and economical at aniron or steel plant, it is preferred to use the products of combustionissuing from furnaces employing blast furnace gas as fuel. For example,the products of combustion from the hot blast stoves used in preheatingthe air-for blast furnaces may very conveniently and cheaply beemployed. It is desirable that these gases contain as much carbondioxide as is convenient. Any sulphur dioxide in these gases should betaken into account, but small quantities of sulphur dioxide are notseriously objectionable.

The products of combustion should be substantially cooled before beingintroduced into the slurry, to prevent difliculty through the productionof steam in the revivification system.

The products of combustion are preferably blown or bubbled through theslurry in cast iron rate cylindrical tank about 3 feet (0.9 meter) indiameter and 15 feet (4.6 meters) tall. It is preferable to use aboutseven such tanks in conjunction, the exit gases from the tank receivingthe gases rich in carbon dioxide passing'through a series of other tanksto efiect the desired reactions.

Each tank has a nitrogen cycle and a hydrogen sulphide cycle. During theoperation of a given tank as the first tank in the'train, the exit gasesfrom this tankare initially nitrogen, which is inert, excess carbondioxide and hydrogen sulphide produced by Reactions (13) and (15). Thesegases are passed into other tanks where both hydrogen sulphideand carbondioxide are absorbed, until the final exit gas is substantially nothingbut nitrogen, which can be exhausted. As the gas treatment continues, a.stage is reached in one of the tanks in which the exit gases are rich inhydrogen sulphide and low in carbon dioxide. Such gases may be withdrawnand utilized for their sulphur content.

-After suflicient carbon dioxide has been absorbed in a particular tankto complete Reactions (13), (14), and (15), theslurry maybe withdrawnfrom this tank and the gas rich in carbon dioxide may be applied toanother tank. The

the tanks of Figure 7 through the inlet pipe GI and the exit gases leavethrough the outlet pipe '62. An inlet header 63 runs across all of thetanks and may be used to carry gas rich in carbon dioxide to any ofthem. Each tank is equipped with a down-flow pipe 64, 65, 86, 61, 68,69, or 10, extending from the inlet header 63 to the bottom of the tank.Each tank also has at its top an up-fiow pipe H, 12, 13, 14, 15, 16, or11, which joins the inlet header 63.

From the up-flow pipe of each tank to the down-flow pipe of the nexttank is a cross-connection 18, 19, 80, M, 82, 83, or 84 (thecrossconnection 84 is a long pipe extending across the back of the tanksin Figure 7). The various elbows and Ts. are provided with suitablecapflanges to permit ready access to the pipes.

Numerous valves are placed to permit change in the direction of gasflow. Between the junction with each downflow pipe and the junction withthe next up-fiow pipe, the inlet header 03 has a valve 85, 86, 81, 88,89, 90, or 9|. Between its junction with the inlet header 83 and itsjunction with its cross-connection, each down-flow pipe has a valve 92,93, 94, 95, 96, 91, or 98. The inlet 8| lies between the valves 85 and92. Between its junction with the inlet header 63 and its junction withits cross-connection, each upfiow pipe has a valve 99, I00, IOI, I02,I03, I04, or I05. Each cross-connection 18, 19, 80, 8I, 82, or 83-has avalve I08, I01, I08, I09, H0, or III, while the cross-connection 84 hastwo valves H2 and I I3. Each tank is connected with the outlet 62through a valve H4, H5, H8, H1, H8, H9, or I20.

If it be assumed that the tank 60 is out of service, having itsrevivified slag removed, for example by taking oif acap-fiange at thebottom, permitting air to enter at the top, and allowing the slurry toflow into any suitable drainage system, the tanks may operate asfollows. Gas high ,vessels such as are shown in Figure 7. Each of the.vessels 54, 55, 58, 51, 58, 59, and is a. sepain carbon dioxide enteringthrough the inlet 6I takes a route through valve 92 and down-flow pipe64 into the bottom of tank 54 and bubbles up through tank 54.

A mixture of carbon dioxide, hydrogen sulphide and nitrogen may issuefrom tank 54. This gas is passed by up-flow pipe II, cross-connection18, including valve I06 in open position, and downflow pipe 65 into thebottom of tank 55. Most of the carbon dioxide and hydrogen sulphide areabsorbed in tank 55, but the gas is passed through up-flow pipe 12,cross-connection I6, including valve I01 in open position, and down-flowpipe 66 into the bottom of tank 56.

In tank 56 the remainder of the carbon dioxide and hydrogen sulphide areabsorbed, and the efliuent gas is substantially nitrogen, which passesthrough valve H6 into outlet 62. During the nitrogen cycle this'efliuent is allowed to escape.

As the blowing of tank 54 continues, more hydrogen sulphide passes overinto tanks 55 and 56, and eventually the quantity of hydrogen sulphidein the eflluent gas from tank 56 becomes appreciable. 'At this point,the effluent gas is led through tank 51 by closing valve H6 anddirecting the gas through up-flow pipe I3, cross-connection 80 (valveI08 in open position) and downfiow pipe Iil into the bottom of tank 51,and then by outlet valve II 1 into outlet 62. With increase in thehydrogen sulphide content of the eilluent gas from tank 51, it may bedesirable to add tank 58 to the train by closing outlet valve Ill andopening cross-connection valve I09 and outlet valve IIB. i

As the blowing of tank 54 proceeds further, the efliuent gas from tank56 (which is being carried to tanks 51 and 58) reaches such a highconcentration of hydrogen sulphide that it can be utilized to recoverthe sulphur. This is the end of the nitrogen cycle and the beginning ofthe hy drogen sulphide cycle. Tanks 51 and 58 are cut out of the trainby opening outlet valve H6 and closing cross-connection valves I08 andI09 and outlet valve H8. The outlet 62 is connected to suitable storageor recovery mechanism.

As the blowing of tank 54 continues still further, the hydrogen sulphidecontent of the eiliuent gas from tank 56 decreases and carbon dioxidebegins to come over into the eiiluent gas from tank 56. This is the endof the hydrogen sulphide cycle and the beginning of another nitrogencycle. Other tanks are then put back in train, for example by openingvalves I08, I09, and H8, and closing valve IIG.

Finally' the contents of tank 54 are completely revivified and gas richin carbon dioxide is led to tank 55 by closing valves 92 and I06 andopening valves 85 and 93. Tank 54 can now be emptied and refilled withslurry to be revivified. At the proper times in the cycle for tank 55,tank 59' is added to the train.

In general, other valves not mentioned during the above discussion arekept closed until it is necessary to open them when other tanks are inservice.

The above discussion is merely illustrative of one manner of using thetanks, and is not intended to limit the disclosure, as other apparatusmay be employed or this apparatus may be used in other ways.

The revivified slag can be removed from the tank in which the process iscompleted, filter pressed or run through a Dorr thickener or similarapparatus, dried and used for further desulphurization of additionalcharges of pig iron.-

The drying may be done in a rotary drier if desired and the chargeissuing from the drier may attain temperatures approximating 1000 C. Atthese temperatures, calcium carbonate is changed to calcium oxide. Thishot discharge material can be placed in suitable containers to conserveits heat content and used as a desulphurizing slag for more pig iron.

It will be evident that the compounds used to revivify the slag inaccordance with the above processes, namely water and carbon dioxide,are the very substances whose presence in substantial quantities isundesirable during desulphurization and which are preferably excludedfrom the desulphurizing vessel. a

The point at which the slag is desulphurized will depend, of course,upon the exact process used. If the desulphuriz'ation is to beaccomplished in stepwise manner, each desulphurizing slagis used twice,as a second slag on one charge and a first slag on the next charge,before it is revivified. It would of course be possible to use the sameslag three or a greater number of times before revivification, but thiswould complicate the process; In any case, when the sulphur content ofthe slag reaches a predetermined value, the slag is separated from themolten pig iron and revivified.

The gas rich in hydrogen sulphide obtained from reviviflcation may beused for its sulphur content. For example, it may be burned tosulphurdioxide by mixing it with suflicient air, and the sulphur dioxidemay be made into sulphuric acid or other suitable compounds. Or, in thepresence of a suitable catalyst, the hydrogen sulphide may be burneddirectly to sulphur trioxide. The hydrogen sulphide may also beconverted into elemental sulphur by combustion with the required amountof air in accordance with the following reaction:

Whether the sulphur be changed to sulphuric acid, recovered as elementalsulphur or in some other form, the value of the resulting product may becredited against the cost of revivifying the slag, and may in some casesmore than pay for the cost of revivification. I

Figure 6 shows, by way of example, a series of steps which may beemployed in the process. The ladle shown at the top of the chart maysuitably contain 100 tons of molten pig iron of say 0.26% sulphurcontent. Into the ladle is charged about 2.5 tons of a firstlime-fluorspar desulphurizing slag containing about 2.40% sulphur(corresponding to about 6% calcium sulphide) This high sulphur contentis due to previous desulphurizing use of the slag subsequent toreviviflcation. After suitable contact between the molten pig iron andthe first desulphurizing slag in the ladle, the slag is separated fromthe pig iron. The first slag now contains, for example, 10.8% sulphur.

The slag is now ground to say 50 mesh per linear inch or allowed toself-disintegrate by slow cooling and pre-selection of the propercomposition. The ground slag is then mixed with water'to form a slurryand treated with a gas high in carbon dioxide, by which the slag isrevivified, and hydrogen sulphide gasdriven off. The hydrogen sulphidegas may be burned in a suitable furnace to liberate sulphur, or,- in thealternative, to form sulphur dioxide. The revivified slurry is nextdewatered and calcined to produce a revivified slag containing, say, 1%of sulphur.

The revivified slag is then supplied to a subsequent charge in the ladleand there used as a second slag for treating pig iron which wasinitially desulphurized with a previous slag. pig iron beforetreatmentwith the'secondslag may have a sulphur content of say 0.05%sulphur, but after treatment, with the second slag its sulphur contentwill drop to perhaps 0.015% sulphur. The sulphur content of the slag, inthe meantime, will increase from about 1% to about 2.40%. This secondslagis then available for use'as a first slag to treat a new charge ofpig iron.

Through both of the desulphurizing, treatments, the ladle is maintainedunder reducing conditions by the presence of carbon and desirably alsoby the positive exclusion of the atmosphere and combustion gases high incarbon dioxide and water vapor. The mixture of oxides of carbon presentin the ladle is predominantly reducing due to the excess of carbon, andalso desirably due to the introduction of harmless reducing gases atsuperatmospheric pressure.

It is contemplated that there will be certain losses of slag during thedesulphurizing process, and that certain small amounts of impurities maybe picked up, both of which features will necessitate additions of freshslag-making materials'from time to time. By the use of properrefractories in the ladle car, by the maintenance of reducing conditionswhen the slag is in contact with the molten pig iron, andby suitabletreatment with carbon dioxide followed by proper processing of' theslurry produced in that operation, the fresh slag-making materialsrequired can be kept to a minimum in order to effect, to'the fullestextent, the economies made possible by repeated use of the slag.

One process of revivifying the slag by driving oil the sulphur as avolatile sulphur component in the form of hydrogen sulphide has justbeen discussed. This process may be varied by treating the powderedslag-at higher temperature with steam and carbon dioxide gas, instead ofcarrying out the process by treating a slurry at moderate temperature.

" molten condition at about 1200 C. to 1400" C. In pig iron at lowercostbut with a higher sulphur There are a number of other processes by whichrevivification may be accomplished. For example, as indicated in Figure6a, sulphur may be removed from the slag directly as sulphur dioxidegas, by maintaining the high-sulphur slag molten and at high temperatureafter, it is removed from the ladle car and blowing air or oxygenthrough the slag. In this way sulphur dioxide will form readily and thesulphur content of the slag may be effectively reduced.

Another process of revivifying the slag, as shown in Figure 6b, is toallow it to cool, and reduce it to a fine powder, as byself-disintegration or by crushing and grinding. A portion of the slagis then roasted in a conventional furnace used for roasting sulphides,desirably to a temperature of about 1000 C. Calcium sulphide is therebychanged to calcium sulphate and some of the sulphur is driven ch assulphur dioxide.

The slag containing calcium sulphate is then mixed with a theoreticalquantity of unroasted slag and melted to cause calcium sulphide andcalcium sulphate to react:

CaS+8CaSO4=4CaO+4SO2 (17) This reaction is carried out with the slag inthis way the greater part of the sulphur from the sulphur-rich slag isdriven oi as sulphur dioxide, and may be used for manufacturingsulphuric acid or in other suitable manner.

A serious diflioulty with both of the last-mentioned processes forrevivifying the desulphurizing slag is that they require that the slagbe maintained molten under oxidizing conditions.

Slags high in lime and calcium' fiuoride'are rather corrosive torefractories other than carbon and; while carbon may be used in theladle car under reducing conditions, it may not be used in operationsinvolving the volatilization of sulphur dioxide whereoxidizingconditions are necessary. It is therefore obligatory to haverecourse to magnesite and similar refractories, and magnesite brick maybe attacked by the slag.

Another process for revivifying the slag, as

indicated in Figure 6c, involves the conversion of the sulphur in theslag to a metal sulphide with the molten slag, known as a matte. Copperis a suitable matte-forming metal; nickel might also be used. A sulphideof the type RxS reacts with a matte-forming metal thus After removal ofthe sulphur from the copper, the copper bath may be used to desulphurizemore slag.

The decision as to whether to revivify the slag by a wet process at lowtemperatures to eliminate hydrogen sulphide or by a dry process at hightemperatures will depend upon the factors prevailing in individualcases. It is considered, however, that the wet process will be moreeconomical in many instances.

Numerous examples have been given herein to aid in practicing theinvention. It is not intended, however, to limit the disclosure byreason of the inclusion of these examples except where limitations areincluded in the claims or indicated by the specification to beessential.

In view of my invention and disclosure variations and modifications tomeet individual whim or particular need will doubtless become evident toothers skilled in the'art, to obtain all or part of the benefits of myinvention without copying the structure shown, and I, therefore, claimall such in so far as they fall within the reasonable spirit and scopeof my invention.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. The process of producing desulphurized pig iron; which comprisessmelting the iron in a coke blast furnace under conditions oftemperature and basicity of the slag suitable to produce capable offorming a molten phase immiscible -content in the iron than thatultimately desired,

transferring the pig iron from the blast furnace to a vessel lined withcarbon, maintaining the pig iron molten in the vessel free from theapplication of additional heat, and treating the molten pig iron in thevessel to reduce its sulphur content with a basic slag under reducingconditions while positigely protecting the slag from oxidizing gases.

' 2. The process of desulphurizing pig iron, which comprises smelting itin a coke blast furnace under' conditions which produce a substantiallyI higher sulphur content than that ultimately desired, transferringthepig iron from the coke blast furnace and subsequentlysubjecting themolten pig iron without application of additional heat under reducingconditions to a basic slag containing fluorspar and lime totalling morethan 50%, the lime alone being not more than 55%, silica and asubstantial quantity of sodium oxide.

3. The process of producing pig iron of low sulphur content, whichcomprises smelting iron ore under conditions which produce pig ironhaving a substantially higher sulphur content than that ultimatelydesired, tapping the pig iron from the blast furnace, and treating thepig iron in a vesselinthe presence of an excess of solid carbon freefrom substantial additions of oxidizing substances, with adesulphurizing agent containing calcium oxide, not more than 55%,fluorspar and silica, the fluorspar and silica totalling more than 25%,while maintaining the pig iron molten without the application ofadditional heat and without forming calcium carbide in the slag.

4. The process of producingpig iron oflow sulphur content, whichcomprises smelting iron ore under conditions which produce pig ironhavinga substantially higher sulphur content than that ultimatelydesired, tapping the pig iron from the blast furnace, and desulphurizingthe pig iron in a vessel in the presence of an excess of solid carbon,free from substantial additions of oxidizing substances; with a slagcontaining calcium oxide, calcium fluoride and silica and capable ofremoving the sulphur from the pig iron until not more than 0.015% ofsulphur remains, while maintaining the pig iron molten at a temperatureof 1400 C. or less, without the application of additional heat andwithout forming calcium carbide in the slag.

5. The process of producing pig iron oflow sulphur content, whichcomprises smelting iron ore under conditions which produce pig ironhaving a substantially higher sulphur content than that ultimatelydesired, tapping the pig iron from the blast furnace, desulphurizing thepig iron in a vessel in the presence of an excess of solid carbon, freefrom substantial additions of oxidizing substances, with a slagcontaining calcium oxide, not more than 55%, calcium fluoride andsilica, the calcium fluoride and silica totalling more than 25%, untilthe sulphur percentage in the slag is more than 250 times the sulphurpercentage in the pig iron and maintainingthe pig iron molten during thedesulphurization at a temperature'of 1400 C. or less without theapplication of additionalheat and without forming calcium carbide in theslag.

6. The process of producing desulphurizd pig iron, whichcomprisessmelting iron ore under conditions which produce pig iron having asubstantially higher sulphur content than that ultimately desired,tapping the pig iron from the blast furnace and desulphurizing the pigiron in a vessel in the presence of an excess of solid carbon by a slagcontaining between 30% and 55% of calcium oxide, between 20% and 50% offluorspar and between and 25% of silica, while maintaining the pig ironmolten, without the application of additional heat and without formingcalcium carbide in the slag. I

7. The process of producing desulphurized pig iron, which comprisessmelting iron ore under conditions which produce pig iron having asubstantially highersulphur content than that ultimately desired,tapping the pig iron from the blast furnace and treating the pig iron ina vessel with a desulphurizing agent containing'fluorspar and silica,the fluorspar and silica totalling treatment exceeds 2.5% sulphur, whilemain taining the pig iron molten during the treatment without theapplication of additional heat and without forming calcium carbide inthe slag.

8. The process of producing desulphurized pig iron, which comprisessmelting iron ore under conditions which produce pig iron having asubstantially higher sulphur content than that ultimately desire'd,tapping the pig iron from the blast furnace, maintaining the pig ironmolten at a temperature below the blast furnace tapping temperature andin a vessel free from the application of additional heat, desulphurizingthe pig iron in the vessel in the presence of solid carbon understrictly deoxidized conditions by a slag containing between 30% and 55%of calcium oxide, between and 50% of fluorspar and between 5% and ofsilica, and agitating the molten reactants during desulphurization.

9. The process of desulphurizing pig iron, which comprises treating acharge of pig iron in molten condition with a slag comprising betweenand 55% of lime, between 20% and of fluorspar and between 5% and 25% ofsilica which removes sulphur from the pig iron until the slag containsmore than 5% sulphur, separating the slag from the molten pig iron, andtreating the slag to lower its sulphur content while the slag is out ofcontact with molten pig iron.

10. The process of desulphurizing molten pig iron produced in a cokeblast furnace, which comprises treating molten pig iron external to thecoke blast furnace with a slag comprising between 30% and of calciumoxide, between 20% and 50% of calcium fluoride and between 5% and 25% ofsilica, separating the sulphur-bearing slag from the desulphurized pigiron, treating the sulphur-bearing slag to lower its sulphur content andreusing the slag for desulphurizing a further charge of pig iron.

11. The process of de sulphurizing pig iron, which comprises treating acharge of pig iron in molten condition in a carbon lining of adesulphurizing vessel with a slag which removes sul-.

phur, concurrently excluding the atmosphere by a noncontaminatingreducing gas, separating the slag from the molten pig iron, treating theslag to lower its sulphur content while the slag is out of contact withthe molten pig iron and reusing the slag to disulphurize a furthercharge of pig iron.

12. The process of desulphurizing pig iron, which comprises treating acharge of pig iron in molten condition in a carbon lining of adesulphurizing vessel, with a slag which removes sulphur, concurrentlyexcluding the atmosphere by carbon monoxide at superatmosphericpressure, separating the slag from the molten pig iron, treating theslag to lower its sulphur content while the slag is out of contact withthe molten pig iron and reusing the slag to desulphurize a furthercharge of pig iron. 7,

13. The process of desulphurizing pig iron, which comprises successivelysubjecting it in molten condition after it leaves the blast furnace todesulphurizing slags comprising between 30% and 55% of calcium oxide,between and 50% of calcium fluoride and between 5% and ,25% of silicaand of progressively decreasing of removing sulphur, separating the slagfrom the pig iron, revivifying the slag to permit its reuse fordesulphurizing more pig iron and recovering the sulphur of the slag aselemental sulphur.

'15. The process of desulphurizing pig iron, which comprises treatingmolten pig iron containing more sulphur than is desired under reducingconditions with a basic slag capable of removing sulphur whileprotecting the pig iron and slag from free oxygen, carbon dioxide andwater vapor, separating the slag from the desulphurized pig iron,treating the sulphur-bearing slag in the presence of the carbon dioxideand w'aterto remove its sulphur content and reusing the slag todesulphurize a further charge of pig iron.

16. The process of desulphurizing pig iron, which comprises treating thepig iron under reducing conditions with a lime slag which is fluid at1200" C., the composition of the slag being adjusted so that the slagwill self-disintegrate when it solidifies and cools, withdrawing theslag from the pig iron and allowing it to disintegrate and treating theslag with water and carbon dioxide to eliminate the sulphur and renderthe slag available for reuse.

17. In the manufacture of steel, the process which comprises smeltingiron ore under conditions which produce pig iron having a substantiallyhigher sulphur content than that ultimately desired, tapping the pigiron from the blast furnace, desulphurizing the pig iron in a vesselunder strictly deoxidized conditions by a slag containingbetween 30% andof calcium oxide, between 20% and 50% of fiuorspar and between 5% and25% of silica until the sulphur content of the pig iron is not more thancapable of takingup sulphur, separating the slag from the iron, bringingthe slag into contact with molten copper under mildly oxidizingconditions, separating the slag from the molten copper and vigorouslyoxidizing the copper to remove the sulphur. a v

19. The process of producing steel, which comprises smelting iron in acoke blast furnaceunder conditions which produce a substantially highersulphur content than the sulphur content ultimately desired,transferring the pig iron excessively high in sulphur from the cokeblast furnace, subsequently treating the molten pig iron direct from thecoke blast furnace with a basic lime slag capable of removing sulphurfrom the pig iron in a carbon lining and in the absence oi' oxidizinggases, transferring the pig iron to a steel-making furnace and therechanging it into steel, revivifying the slag to reduce its sulphurcontent and reusing the slag to desulphurize a further charge of pigiron.

20. The process of producing steel, which comprises smelting iron in acoke blast furnace under conditions which produce a substantially highersulphur content than the sulphur content ultimately desired,transferring the, pig 'iron excessively high in sulphur from the cokeblast furnace, subsequently treating the molten pig iron underpredominantly reducing conditions in the presence of an excess of carbonwith a basic slag comprising between 30% and 55% of calcium oxide,between 20% and 50% of calcium fluoride and between 5% and 25% ofsilica, capable of absorbing sulphur until the sulphur content of theslag exceeds.5%,.transferring the pig iron to a steel-making .furnaceand there changing it to steel, revivifying the slag to reduce itssulphur .content and reusing the Slog to desulphurize a further chargeof pig iron.

21. The process of revivifying a pig iron desulphurizing slag containinga substantial amount of calcium sulphide or similar alkaline earthsulphide, which consists in treating the slag after separation from themolten pig iron with water and carbon dioxide,- thereby eliminating thesulphur as hydrogen sulphide.

22. The process of revivifying a pig iron desulphurizing slag containinga substantial amount of calcium sulphide or similar alkaline earthsulphide, which comprises reducing the slag to a powder, mixing the slagwith water and subjecting the mixture of water and powdered slag to theaction of carbon dioxide gas.

v23. The process of revivifying a pig iron desulphurizing slagcontaining a substantial amount of calcium sulphide or similar alkalineearth sulphide which comprises reducing the slag to a powder, mixing theslag with water and subjecting the mixture of water and powdered slag tothe action of the products of combustion of blast furnace gas. I

24. The process of revivifying a pig iron desulphurizing slag containinga substantial amount of calcium sulphide or similar alkaline earthsulphide, which consists in treating the slag with the products ofcombustion of blast furnace gas. 1 v

25. The process 01' revivifying a pig iron desulphurizing slagcontaining an alkaline earth sulphide which comprises reducing the slagto a powder by self-disintegration, making the slag into a slurry withwater, bubbling gas containing carbon dioxide through the slurry, anddewatering and drying the slurry.

26. The process of revivifying a pig iron desulphurizing slag containingan alkaline earth sulphide which comprises treating the slag with carbondioxide and water to generate hydrogen phide, which comprises treatingthe slag with carbon dioxide and water to generate hydrogen sulphide,and burning the hydrogen sulphide with the required amount of oxygen toliberate elemental sulphur.

28. The process of revivifying pig iron desulphurizing slagcontainingalkaline earth or alkali sulphides, which comprises bringing the slag inmolten condition into contact with a matteforming metal under mildlyoxidizing conditions, in separating the slag from the metal, removingthe sulphur from the matte and reusing the metal for thedesulphurization of further slag.

29. In the process of revivifying a sulphurcontaining slag, the stepwhich consists in removing sulphur from the slag by cohtact with amatte-forming metal.

30. In the process of revivifying a sulphur-containing slag, the stepwhich consists in removing sulphur from the slag by bringing the slaginto contact with molten copper.

31. A basic desulphurizing slag comprising lime, fluorspar and silica,which is free flowing above 1200 C. and. which contains more than 5% ofsulphur after use for desulphurlzing pig iron.

33. A slag which has been used for desulphurizing pig iron comprisingfrom 30% to 55% of lime, from 20% to of fluorspar and from 5% to 25% ofsilica, and more than 2.5% sulphur, substantially free from calciumcarbide.

34. A slag which has been used for desulphurizing pig iron comprisingabout 45% of lime,

about 40% of fluorspar, about 15% of silica, and

more than 2.5% sulphur.

35. A slag which has been used for desulphurizing pig iron comprisinglime in excess of 30%, fluorspar in excess of 20%, silica in excess of5%, alumina from 1% to 5%, and more than about 2.5% of sulphur,substantially free from calcium carbide.

36. The process of producing desulphurized pig iron which comprisessmelting iron ore to produce pig iron containing more sulphur than thecontent ultimately desired, removing the pig iron from the blastfurnace, subsequently maintaining the pig iron molten in a vessel linedwith refractory containing magnesia as its principal ingredient freefrom the application of additional heat and treating the pig iron in thevessel as a wholly separate operation subsequent to the production ofthe pig iron under reducing conditions with a slag containing fluorsparnot less than 20%, lime in an amount exceeding the fluorspar but notmore than together with silica and another oxide, in addition to thelime, of the type ReO, where R is a metal of the group consisting ofalkaline earth metals and alkali metals and :c is a numeral determinedby the valence of the metal, until the sulphur content of the slagformed during the treatment exceeds 2.5% sulphur.

RUSSELL PEARCE HEUER.

